Welding Procedure Specification — What It Is and Why It Matters
A welding procedure specification (WPS) is a formal written document that defines exactly how a specific weld is to be made. It specifies every essential variable: welding process, base metal, filler metal, preheat and interpass temperatures, shielding gas, joint design, welding positions, electrical parameters, and technique details.
A WPS is developed by welding engineers and qualified through physical testing — a procedure qualification record (PQR) documents the actual test weld made per the WPS parameters and the mechanical test results (tensile, bend, and impact tests) that prove the procedure produces acceptable welds.
On code work, every production weld must be made in accordance with a qualified WPS. The WPS ensures consistency, quality, and traceability — any welder following the same WPS should produce welds with the same properties. Deviating from the WPS without engineering approval is a code violation that can require the work to be rejected and redone.
Frequently Asked Questions
Does every weld need a WPS?
On code-governed work (structural steel per AWS D1.1, pressure vessels per ASME Section IX, pipelines per API 1104), yes — every production weld must be made per a qualified WPS. For non-code work (hobby, artistic, general fabrication not governed by a code), a formal WPS is not typically required.
What is the difference between a WPS and a PQR?
The WPS is the instruction document — it tells the welder how to make the weld. The PQR (Procedure Qualification Record) is the evidence document — it records the actual test weld parameters and the mechanical test results that prove the WPS produces acceptable welds. The PQR qualifies and supports the WPS.